1. Field of the Invention
The present invention relates to fluorescence based sensors and, more particularly, to fluorescence based sensors with mirrored cavities for improved sensitivity.
2. Background of the Related Art
Pollution is one of the major problems in the modern industrialized world. In the United States, industry is the greatest source of pollution, accounting for more than half the volume of all water pollution and for the most deadly pollutants. Some 370,000 manufacturing facilities use huge quantities of freshwater to carry away wastes of many kinds. The waste-bearing water is discharged into streams, lakes, or oceans. In its National Water Quality Inventory, the U.S. Environmental Protection Agency concluded that approximately 40% of the nation's surveyed lakes, rivers, and estuaries were too polluted for such basic uses as drinking supply, fishing, and swimming. Pollution not only increases the concentrations of harmful substances, but also changes the pH and the levels of CO2 and oxygen dissolved in a body of water, thereby disrupting the water's ecological balance, killing off some plant and animal species while encouraging the overgrowth of others.
Another environmental problem is global warming. The majority of scientists studying climate changes believe that global warming is likely caused by increasing amount of greenhouse gases (mostly CO2) discharged into the environment by human activity. Global warming has numerous deleterious effects, such as rising sea levels, changing the amount and pattern of precipitation, and increasing the intensity of extreme weather events and changing agricultural yields. The rise in CO2 levels, while contributing to global warming, is also creating ocean acidification at an alarming rate as the oceans collect more CO2. Warming water and increasingly acidic seas will further change the global ecosystem.
Scientists studying the association between Earth climate and extinctions stated that “the global temperatures predicted for the coming centuries may trigger a new ‘mass extinction event’, where over 50 percent of animal and plant species would be wiped out.” Many of the species especially at risk are Arctic and Antarctic fauna because those species usually rely on cold weather conditions to survive and to reproduce. This will adversely affect the existing local fisheries upon which humans depend. Additionally, it has been shown that climate change due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions have stopped. Concerted action is required to minimize the effect of global warming and most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.
Meanwhile, governments are in the process of implementing requirements for systems to monitor pCO2 levels and for alleviating the severity of the effects of global warming. Therefore, there is currently an urgent need for small, low-cost, calibration-free pCO2 sensing systems for ocean monitoring.